Davis has been training at Upton Boxing Center since he was five years old.[5][6] Davis is trained by Calvin Ford who was the inspiration for the character Dennis "Cutty" Wise on the hit HBO television series, The Wire.[7][8] Davis had a very successful amateur career, winning many national championships. He won the 2012 National Golden Gloves Championship,[9] three straight National Silver Gloves Championships from 2006–2008,[10] two National Junior Olympics gold medals, two National Police Athletic League Championships, and two Ringside World Championships, among others. Davis finished his illustrious amateur career with an impressive record of 206–15.[11]

Davis made his debut at the age of 18 on February 22, 2013 against Desi Williams, who had a professional record of no wins and 4 losses, all by stoppage. The fight took place at the D.C. Armory in Washington on the undercard of IBF super lightweight fight between Lamont Peterson and Kendall Holt. Davis won the bout via 1st round knockout. By August 2014, Davis had recorded 8 wins and no losses, with all wins coming inside the distance. Davis was taken the six round distance for the first time in October 2014 against veteran 28 year old German Meraz (47–31–1, 25 KOs). Davis knocked Meraz down in rounds 3 and 5, and went on to win a unanimous decision, winning all rounds on the three scorecards (60–52, 60–52, 60–52).

On November 15, 2016 ESPN announced that Davis would challenge for the IBF junior lightweight title against undefeated José Pedraza (22–0, 12 KOs) on January 14, 2017 at the Barclays Center in Brooklyn on Showtime. The fight would take place as an undercard fight to the super middleweight world title unification fight between James Degale and Badou Jack. The IBF granted Pedraza an exception to fight Davis, as he had a mandatory fight against British boxer Liam Walsh looming. prior to the fight being announced, Mayweather promotions matchmaker tried to make a deal for Davis to fight titleholder Jason Sosa.[20] Davis defeated Pedraza in a seventh-round knockout to win the IBF junior lightweight title.[21] After the fight, Davis said that he had studied the early career of his promoter and mentor, Floyd Mayweather Jr., in order to stay composed. He said, "I had a lot of experience [from the amateur ranks], but I learned how to keep my composure. Floyd told me to stay calm, and I studied Floyd Mayweather [videos] when he was 'Pretty Boy.' My uppercut was my best shot, and it was landing all night. It felt really good to fight the way I did. I could take it and dish it out." Mayweather Jr. himself enthusiastically branded his protégé as the future of boxing. For the fight, Davis earned $75,000 compared to Pedraza, who earned the lions share of $225,000, in what was his third defence. At the time of stoppage, Davis was ahead 59–55 on all three judges scorecards.[22] The bout took place on the undercard of the super middleweight unification fight between James DeGale and Badou Jack and averaged 344,000 viewers.[23]

On May 7, 2017 it was announced Davis would travel to London, England for his first title defence. The news came from Frank Warren, promoter of challenger Liam Walsh (21–0, 14 KO), who was also ranked number 1 by the IBF. The fight was scheduled to take place on May 20, 2017 and billed as 'Show me the Money'.[24][25] At the official weigh in on May 19, Davis made weight on his third attempt. His first attempt, although he was naked, he weighed two ounces over. He was then given the two hours to attempt to lose the extra weight, although he came back earlier thinking he had lost it. He eventually met the limit of 130 pounds on his third attempt.[26] Davis stopped Walsh in the third-round to retain his IBF title. After two cagey rounds, which were controlled by Davis, he came out with power punches at the start of the third. Walsh's legs looked to give way and David pounced with accurate hooks to the head, eventually dropping Walsh. Walsh beat the count on unsteady legs. The fight resumed and Davis went on the attack again, connected with every shot he threw, forcing referee Michael Alexander to stop the fight. The time of stoppage was 2 minutes and 11 seconds of round 3.[27] Many at ringside believed the stoppage was premature, including Walsh, "That was a bad stoppage. He's very fast and very active but it was too quick. He won fair and square but in England sometimes they stop the fight too early." Davis believed he would have caught Walsh eventually.[28][29] The fight was shown live on Showtime in the USA averaging 228,000 viewers and peaking at 253,000 viewers.[30]

According to TMZ Sports in early July 2017, it was reported that Davis would feature in the co-main event of Floyd Mayweather Jr. vs. Conor McGregor on August 26, 2017 at the T-Mobile Arena in Paradise, Nevada.[31] On July 29, The Ring Magazine reported that Davis would likely defend his IBF title against former WBO champion Román 'Rocky' Martínez, whose last fight was a knockout loss to Vasyl Lomachenko in June 2016.[32] On August 10, Ringtv reported that Davis would instead fight unbeaten prospect Francisco Fonseca (19-0-1, 13 KOs), who at the time was ranked number 7 by the IBF. According to some sources, the potential fight with Martínez was dropped due to notice and Martínez would not have had enough time to make the 130 pound limit.[33] Prior to the fight being announced, the IBF had ordered Fonseca to fight their number 3 ranked Billy Dib (42-4, 24 KOs) in a final eliminator, as they were the two highest ranked available.[34] At the weigh in, Fonseca came in at the 130 pound limit. Davis showed up an hour late and came in at 132 pounds, 2 pounds over the weight limit. Davis declined to weigh in after two hours, forcing the IBF to strip him of the title. The title was declared vacant, but the title would be still up for grabs if Fonseca secured victory.[35] In what was billed as an easy fight for Davis, he won the fight via knockout in round 8, with the ending being controversial. The final punch appeared to be an illegal punch to the back of the head to Fonseca and referee Russell Mora counted him out 39 seconds into the round. After the fight, Davis mocked Fonseca.[36] Fonseca appeared hurt before the knockout blow, which Davis, who was being booed by the crowd, explained to Jim Gray of Showtime in the post fight interview, “I actually caught him with a body shot before that and he was hurt. So he took advantage of me hitting him in the back of his head and went down.” With the win, Davis scored his 10th straight knockout victory. Due to Davis winning the fight, the IBF title remained vacant.[37][38] For the fight, Davis earned a purse of $600,000 compared to the amount $35,000 that Fonseca received.[39]

On November 15, 2017 Leonard Ellerbe, CEO of Mayweather Promotions announced that Davis would be making his in ring return in the first quarter of 2018 alongside stablemate Badou Jack. He also revealed that Davis would fight a high-level opponent.[40] According to Mayweather Promotions CEO Leonard Ellerbe, Davis would remain at super featherweight and likely challenge for a world title in 2018.[41] On January 24, 2018 Showtime announced that Davis would next appear on television on the undercard of Broner vs. Vargas on April 21 at the Barclays Center in Brooklyn.[42] A day later, Ellerbe stated a deal was close to being reached for Davis to fight Australian former world champion and IBF #3 Billy Dib (43-4, 24 KOs, 2 NC) in what would be an IBF eliminator. A purse bid, which was due to take place on January 25 was postponed to February 6.[43] On February 21, it was reported by ESPN, the fight would not happen. Instead it was stated Davis's likely opponent would be former featherweight champion Jesús Cuellar (28-2, 21 KOs). On March 5, the fight was finalized for the vacant WBA 'Super' super featherweight title.[44] In front of 13,964 in attendance, Davis became a two-time world champion, knocking out Cuellar in round 3. Davis first knocked down Cuellar in round 2 courtesy of a left hook to the body and then put him down twice in round 3 to get the stoppage. Referee Benjy Esteves Jr. stopped the action at the 2:45 mark. Davis landed 49% of his power shots in the fight. Both boxers earned $350,000 apiece. After the fight, Davis stated he wanted to unify with the winner of Tevin Farmer vs. Billy Dib, which would be contested for the IBF belt, the same belt Davis was stripped off.[45][46][47] The bout opened Showtime’s broadcast and averaged 460,000 viewers and peaked at 527,000 viewers.[48]

On September 19, 2017 an arrest warrant was issued for Davis, who was being accused of first-degree aggravated assault. According to Maryland court records, the alleged incident took place on August 1, 2017 but did not indicate who was involved or what happened. An amount of $100,000 unsecured bond was posted for Davis' release. Davis was due to appear in court on October 19.[49] The charge was later changed to misdemeanor second-degree assault, which carries a maximum potential sentence of 10 years or a fine of $2,500 or both. At the court, Anthony Wheeler, a childhood friend, complained that Davis punched him on the side of the head with a 'gloved fist'. He then stated he was diagnosed with a concussion in hospital. The incident took place at the Upton Boxing Center in West Baltimore. It was said that Davis would stand trial on November 29, 2017.[50] In court, the charges were dropped by Wheeler. The Baltimore Sun stated that Davis and Wheeler both embraced and walked out of the courtroom together.[51]